The present invention relates to a device for collecting filtrate samples from a pulp suspension, comprising a piston rod arranged, when actuated by a cylinder, to carry out a reciprocating movement in a jacket and supporting a filter which is adapted, when in an extended position, to catch a sample.
In the paper and cellulose industry samples are generally collected from a pulp suspension for the purpose of supervising and controlling the process proper. The samples are analysed for determination of parameters relating to the fibres or to the liquid, i.e. the filtrate, with the intention to determine pH-value, H2O2-value etcetera. However, the devices used tend to-get clogged by fibres in the pulp suspension. Especially in devices used for on line-measurement in processes it is important that the cleaning and washing of the sampling equipment satisfy the requirements stipulated. The problem in this connection is that those prior art devices require a regular back-flush with air or water to prevent clogging.
The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a filtrate sampler designed so as to automatically clean itself during the sampling process proper with the aid of a reciprocating movement in a jacket.
The features characterizing the invention are set out in the attached claims.
Thanks to the invention there has now been provided a device for collecting filtrate samples of the type mentioned above which in an excellent manner fulfills its purposes and at the same time is both simple and cheap to manufacture. Preferably the sampling device comprises a pneumatic cylinder the piston rod of which is provided with a filter carrying out a reciprocating movement in a jacket when actuated by the cylinder. The filter does basically consist of a number of wires mounted close to each other and having such a configuration that fibres will automatically be scraped away when the pneumatic cylinder retracts the piston rod carrying the filter into said jacket. There is in this way no need to clean the filter with air or water, instead the cleaning takes place when the filter is retracted from an extended position to an inner position in the jacket. When this has taken place the filter returns again out into the pulp suspension in order to catch another sample. The frequency of the operation is determined by inter alia the type of pulp concerned.